def permHelper(nums, chosen):
    print('permHelper(', nums, ', ', chosen, ')', sep = "")
    if len(nums) == 0:
        print(chosen)
    else:
        for i in range(len(nums)):
            # choose
            n = nums[i]
            chosen.append(n)
            nums = nums[:i] + nums[i+1:]

            # explore
            permHelper(nums, chosen)

            # un-choose
            nums.insert(i, n)
            chosen = chosen[:-1]

def permute(s):
    permHelper(s, [])

permute([1,2])